local Revision = require("git.core.revision")
local diff = require("git.diff")
local object = require("git.object")
local repo = require("git.core.repo")
local status = require("git.core.status")
local util = require("git.core.util")

local M = {}

---@type ow.Git.StatusView.Placement[]
M.PLACEMENTS = { "sidebar", "split", "current" }

---@type ow.Git.Status.Section[]
local SECTIONS = { "untracked", "unstaged", "staged", "unmerged" }
local WINDOW_WIDTH = 50

---@param r ow.Git.Repo
---@return string
local function buf_name_for(r)
    return r.worktree .. "/Git Status"
end

---@alias ow.Git.StatusView.Placement "sidebar"|"split"|"current"

---@class ow.Git.StatusView.Header
---@field is_header true
---@field section ow.Git.Status.Section

---@alias ow.Git.StatusView.Item ow.Git.Status.Row | ow.Git.StatusView.Header

---@class ow.Git.StatusView.State
---@field repo ow.Git.Repo
---@field placement ow.Git.StatusView.Placement
---@field lines table<integer, ow.Git.StatusView.Item>
---@field win integer?
---@field unsubscribe fun()?

---@type table<integer, ow.Git.StatusView.State>
local state = {}

local group =
    vim.api.nvim_create_augroup("ow.git.status_win", { clear = true })
local ns = vim.api.nvim_create_namespace("ow.git.status_win")

---@return integer? win
---@return integer? bufnr
local function find_view()
    for _, win in ipairs(vim.api.nvim_tabpage_list_wins(0)) do
        local buf = vim.api.nvim_win_get_buf(win)
        if vim.bo[buf].filetype == "gitstatus" then
            return win, buf
        end
    end
end

---@param win integer?
---@return boolean
local function valid_in_current_tab(win)
    if not win or not vim.api.nvim_win_is_valid(win) then
        return false
    end
    return vim.api.nvim_win_get_tabpage(win)
        == vim.api.nvim_get_current_tabpage()
end

---@param s ow.Git.StatusView.State
---@return integer?
local function win_for(s)
    if valid_in_current_tab(s.win) then
        return s.win
    end
    local win = find_view()
    s.win = win
    return win
end

---@param row ow.Git.Status.Row
---@return string line
---@return string hl_group
---@return integer hl_len
local function format_row(row)
    local entry = row.entry
    local orig
    if entry.kind == "changed" then
        ---@cast entry ow.Git.Status.ChangedEntry
        orig = entry.orig
    end
    local label = orig and (orig .. " -> " .. entry.path) or entry.path
    local mark = status.mark_for(entry, row.side)
    return string.format("  %s %s", mark.char, label), mark.hl, #mark.char
end

---@param section ow.Git.Status.Section
---@return string
local function display_name(section)
    return (section:gsub("^%l", string.upper))
end

---@param bufnr integer
---@param r ow.Git.Repo
local function render(bufnr, r)
    local status = r.status
    local branch = status.branch
    local lines = {}
    local marks = {}
    local meta = {}

    local function label(row, len)
        table.insert(marks, { row = row, col = 0, end_col = len, hl = "Label" })
    end

    local repo_line = vim.fn.fnamemodify(r.worktree, ":t")
    table.insert(lines, repo_line)
    table.insert(marks, {
        row = #lines - 1,
        col = 0,
        end_col = #repo_line,
        hl = "Directory",
    })

    table.insert(lines, "Branch: " .. (branch.head or "?"))
    label(#lines - 1, 6)

    if branch.upstream then
        local up = "Upstream: " .. branch.upstream
        local extras = {}
        if branch.ahead > 0 then
            local col = #up + 1
            up = up .. " +" .. branch.ahead
            table.insert(extras, {
                col = col,
                end_col = #up,
                hl = "GitUnpushed",
            })
        end
        if branch.behind > 0 then
            local col = #up + 1
            up = up .. " -" .. branch.behind
            table.insert(extras, {
                col = col,
                end_col = #up,
                hl = "GitUnpulled",
            })
        end
        table.insert(lines, up)
        local row = #lines - 1
        label(row, 8)
        for _, e in ipairs(extras) do
            e.row = row
            table.insert(marks, e)
        end
    end

    table.insert(lines, "")

    for _, section in ipairs(SECTIONS) do
        local rows = status:rows(section)
        if #rows > 0 then
            local name = display_name(section)
            local header = string.format("%s (%d)", name, #rows)
            table.insert(lines, header)
            local header_row = #lines - 1
            meta[#lines] = { is_header = true, section = section }
            label(header_row, #name)
            table.insert(marks, {
                row = header_row,
                col = #name + 2,
                end_col = #header - 1,
                hl = "Number",
            })
            for _, row in ipairs(rows) do
                local line, hl, hl_len = format_row(row)
                table.insert(lines, line)
                meta[#lines] = row
                table.insert(marks, {
                    row = #lines - 1,
                    col = 2,
                    end_col = 2 + hl_len,
                    hl = hl,
                })
            end
            table.insert(lines, "")
        end
    end

    util.set_buf_lines(bufnr, 0, -1, lines)
    vim.api.nvim_buf_clear_namespace(bufnr, ns, 0, -1)
    for _, m in ipairs(marks) do
        vim.api.nvim_buf_set_extmark(bufnr, ns, m.row, m.col, {
            end_col = m.end_col,
            hl_group = m.hl,
        })
    end
    state[bufnr].lines = meta
end

---@param bufnr integer
local function refresh(bufnr)
    local s = state[bufnr]
    if not s or not vim.api.nvim_buf_is_valid(bufnr) then
        return
    end
    render(bufnr, s.repo)
end

---@param bufnr integer
---@return ow.Git.StatusView.State?
---@return ow.Git.StatusView.Item?
local function current_entry(bufnr)
    local s = state[bufnr]
    if not s then
        return nil, nil
    end
    local lnum = vim.api.nvim_win_get_cursor(0)[1]
    return s, s.lines[lnum]
end

---@class ow.Git.StatusView.Pane
---@field buf integer
---@field name string?

---@param r ow.Git.Repo
---@param path string
---@return ow.Git.StatusView.Pane
local function head_pane(r, path)
    local rev = Revision.new({ base = "HEAD", path = path })
    return {
        buf = object.buf_for(r, rev),
        name = object.format_uri(rev),
    }
end

---@param r ow.Git.Repo
---@param path string
---@return ow.Git.StatusView.Pane
local function worktree_pane(r, path)
    local buf = vim.fn.bufadd(vim.fs.joinpath(r.worktree, path))
    vim.fn.bufload(buf)
    return { buf = buf, name = nil }
end

---@param s ow.Git.StatusView.State
---@param path string
---@return ow.Git.StatusView.Pane
local function index_pane(s, path)
    local rev = Revision.new({ stage = 0, path = path })
    return {
        buf = object.buf_for(s.repo, rev),
        name = object.format_uri(rev),
    }
end

---@param s ow.Git.StatusView.State
---@param row ow.Git.Status.Row
---@return ow.Git.StatusView.Pane?
local function older_pane(s, row)
    local entry = row.entry
    if row.section == "staged" then
        ---@cast entry ow.Git.Status.ChangedEntry
        if entry.staged == "added" then
            return nil
        end
        return head_pane(s.repo, entry.orig or entry.path)
    end
    if row.section == "unstaged" then
        return index_pane(s, entry.path)
    end
    return nil
end

---@param s ow.Git.StatusView.State
---@param row ow.Git.Status.Row
---@return ow.Git.StatusView.Pane?
local function newer_pane(s, row)
    local entry = row.entry
    if row.section == "staged" then
        ---@cast entry ow.Git.Status.ChangedEntry
        if entry.staged == "deleted" then
            return nil
        end
        return index_pane(s, entry.path)
    end
    if row.section == "unstaged" then
        ---@cast entry ow.Git.Status.ChangedEntry
        if entry.unstaged == "deleted" then
            return nil
        end
        return worktree_pane(s.repo, entry.path)
    end
    if row.section == "untracked" then
        return worktree_pane(s.repo, entry.path)
    end
    return nil
end

---@param target_win integer
---@param dir "left"|"right"
---@return integer
local function vsplit_at(target_win, dir)
    local win = vim.api.nvim_open_win(
        vim.api.nvim_win_get_buf(target_win),
        true,
        { split = dir, win = target_win }
    )
    vim.api.nvim_win_call(win, function()
        vim.cmd("setlocal winfixwidth<")
    end)
    vim.cmd.clearjumps()
    return win
end

---@param status_win integer
---@return integer?
local function previous_target_win(status_win)
    local n = vim.fn.winnr("#")
    if n == 0 then
        return nil
    end
    local win = vim.fn.win_getid(n)
    if win == 0 or win == status_win or not valid_in_current_tab(win) then
        return nil
    end
    local cfg = vim.api.nvim_win_get_config(win)
    if cfg.relative and cfg.relative ~= "" then
        return nil
    end
    return win
end

---@param status_win integer
---@param keep integer
local function close_other_diff_wins(status_win, keep)
    for _, win in ipairs(vim.api.nvim_tabpage_list_wins(0)) do
        if win ~= status_win and win ~= keep and vim.wo[win].diff then
            pcall(vim.api.nvim_win_close, win, false)
        end
    end
end

---@param s ow.Git.StatusView.State
---@param row ow.Git.Status.Row
---@param focus_left boolean
local function view_row(s, row, focus_left)
    local status_win = win_for(s)
    if not status_win then
        return
    end

    local left = older_pane(s, row)
    local right = newer_pane(s, row)
    if not left and not right then
        util.warning(
            "no content for %s row: %s",
            row.section,
            row.entry.path
        )
        return
    end

    if s.placement ~= "sidebar" then
        local pane = right or left
        ---@cast pane -nil
        vim.cmd.normal({ "m'", bang = true })
        vim.api.nvim_win_set_buf(status_win, pane.buf)
        if pane.name then
            util.set_buf_name(pane.buf, pane.name)
        end
        return
    end

    local target = previous_target_win(status_win)
    if not target then
        target = vsplit_at(status_win, "right")
    end
    close_other_diff_wins(status_win, target)
    vim.api.nvim_win_set_width(status_win, WINDOW_WIDTH)
    vim.api.nvim_win_call(target, function()
        vim.cmd.diffoff()
    end)

    if not (left and right) then
        local side = right or left
        ---@cast side ow.Git.StatusView.Pane
        vim.api.nvim_win_set_buf(target, side.buf)
        if side.name then
            util.set_buf_name(side.buf, side.name)
        end
        vim.api.nvim_set_current_win(focus_left and target or status_win)
        return
    end
    ---@cast left ow.Git.StatusView.Pane
    ---@cast right ow.Git.StatusView.Pane

    vim.api.nvim_win_set_buf(target, right.buf)
    if right.name then
        util.set_buf_name(right.buf, right.name)
    end

    local older = left.name or vim.api.nvim_buf_get_name(left.buf)
    local left_win
    vim.api.nvim_win_call(target, function()
        diff.split({
            target = older,
            mods = { vertical = true },
        })
        left_win = vim.api.nvim_get_current_win()
    end)
    vim.api.nvim_set_current_win(focus_left and left_win or status_win)
end

---@param focus_left boolean
local function preview_or_open(focus_left)
    local s, item = current_entry(vim.api.nvim_get_current_buf())
    if not s or not item or item.is_header then
        return
    end
    ---@cast item ow.Git.Status.Row
    view_row(s, item, focus_left)
end

local function action_stage()
    local s, item = current_entry(vim.api.nvim_get_current_buf())
    if not s or not item then
        return
    end
    local paths = {}
    if item.is_header then
        if item.section == "staged" or item.section == "ignored" then
            return
        end
        for _, row in ipairs(s.repo.status:rows(item.section)) do
            table.insert(paths, row.entry.path)
        end
    else
        ---@cast item ow.Git.Status.Row
        if item.section == "staged" then
            return
        end
        table.insert(paths, item.entry.path)
    end
    if #paths == 0 then
        return
    end
    local args = { "add", "--" }
    vim.list_extend(args, paths)
    util.git(args, {
        cwd = s.repo.worktree,
        on_exit = function(result)
            if result.code ~= 0 then
                util.error("git add failed: %s", vim.trim(result.stderr or ""))
            end
        end,
    })
end

local function action_unstage()
    local s, item = current_entry(vim.api.nvim_get_current_buf())
    if not s or not item then
        return
    end
    local rows
    if item.is_header then
        if item.section ~= "staged" then
            return
        end
        rows = s.repo.status:rows("staged")
    else
        ---@cast item ow.Git.Status.Row
        if item.section ~= "staged" then
            return
        end
        rows = { item }
    end
    ---@cast rows ow.Git.Status.Row[]
    if #rows == 0 then
        return
    end
    local args = { "restore", "--staged", "--" }
    for _, row in ipairs(rows) do
        local entry = row.entry
        if entry.kind == "changed" then
            ---@cast entry ow.Git.Status.ChangedEntry
            if entry.orig then
                table.insert(args, entry.orig)
            end
        end
        table.insert(args, entry.path)
    end
    util.git(args, {
        cwd = s.repo.worktree,
        on_exit = function(result)
            if result.code ~= 0 then
                util.error(
                    "git restore --staged failed: %s",
                    vim.trim(result.stderr or "")
                )
            end
        end,
    })
end

local function action_discard()
    local s, item = current_entry(vim.api.nvim_get_current_buf())
    if not s or not item or item.is_header then
        return
    end
    ---@cast item ow.Git.Status.Row
    if item.section == "staged" then
        util.warning("file has staged changes, unstage first with 'u'")
        return
    end
    local entry = item.entry
    local path = entry.path

    local prompt, action
    if item.section == "untracked" then
        local is_dir = path:sub(-1) == "/"
        prompt = string.format(
            "Delete untracked %s %s?",
            is_dir and "directory" or "file",
            path
        )
        action = function()
            local target = vim.fs.joinpath(s.repo.worktree, path)
            local rc = vim.fn.delete(target, is_dir and "rf" or "")
            if rc ~= 0 then
                util.error("failed to delete %s", path)
            end
            refresh(vim.api.nvim_get_current_buf())
        end
    elseif item.section == "unstaged" then
        prompt = string.format("Discard changes to %s?", path)
        action = function()
            util.git({ "checkout", "--", path }, {
                cwd = s.repo.worktree,
                on_exit = function(result)
                    if result.code ~= 0 then
                        util.error(
                            "git checkout failed: %s",
                            vim.trim(result.stderr or "")
                        )
                    end
                end,
            })
        end
    else
        return
    end

    if vim.fn.confirm(prompt, "&Yes\n&No", 2) == 1 then
        action()
    end
end

---@param placement ow.Git.StatusView.Placement
local function action_help(placement)
    local lines = { "git status view" }
    if placement == "sidebar" then
        table.insert(lines, "  <Tab>          preview diff (keep focus)")
        table.insert(lines, "  <CR>           open diff (focus left pane)")
        table.insert(lines, "  <2-LeftMouse>  open diff (focus left pane)")
    else
        table.insert(lines, "  <CR>           open file")
        table.insert(lines, "  <2-LeftMouse>  open file")
    end
    table.insert(lines, "  s              stage file")
    table.insert(lines, "  u              unstage file")
    table.insert(
        lines,
        "  X              discard worktree changes (untracked: delete file)"
    )
    table.insert(lines, "  R              refresh")
    table.insert(lines, "  g?             show this help")
    print(table.concat(lines, "\n"))
end

---@param bufnr integer
---@param placement ow.Git.StatusView.Placement
---@return integer win
local function place(bufnr, placement)
    local split
    if placement == "sidebar" then
        split = "left"
    elseif placement == "current" then
        split = false
    end
    local win = util.place_buf(bufnr, split)
    vim.wo[win].number = false
    vim.wo[win].relativenumber = false
    vim.wo[win].wrap = false
    vim.wo[win].signcolumn = "no"
    vim.wo[win].cursorline = true
    if placement == "sidebar" then
        vim.wo[win].winfixwidth = true
        vim.api.nvim_win_set_width(win, WINDOW_WIDTH)
    end
    return win
end

---@param bufnr integer
---@param r ow.Git.Repo
---@param placement ow.Git.StatusView.Placement
---@param win integer?
local function setup_buffer(bufnr, r, placement, win)
    state[bufnr] = {
        repo = r,
        placement = placement,
        lines = {},
        win = win,
    }

    local function k(lhs, rhs, desc)
        vim.keymap.set(
            "n",
            lhs,
            rhs,
            { buffer = bufnr, silent = true, desc = desc }
        )
    end
    k("<CR>", function()
        preview_or_open(true)
    end, "Open")
    k("<2-LeftMouse>", function()
        preview_or_open(true)
    end, "Open")
    k("s", action_stage, "Stage file")
    k("u", action_unstage, "Unstage file")
    k("X", action_discard, "Discard worktree changes")
    k("R", function()
        r:refresh()
    end, "Refresh")
    k("g?", function()
        action_help(state[bufnr].placement)
    end, "Help")

    state[bufnr].unsubscribe = r:on("change", function()
        refresh(bufnr)
    end)
    vim.api.nvim_create_autocmd("BufEnter", {
        buffer = bufnr,
        group = group,
        callback = function()
            r:refresh()
        end,
    })
    vim.api.nvim_create_autocmd({ "BufWipeout", "BufDelete" }, {
        buffer = bufnr,
        group = group,
        callback = function()
            local s = state[bufnr]
            if not s then
                return
            end
            if s.unsubscribe then
                s.unsubscribe()
            end
            state[bufnr] = nil
        end,
    })
end

---@param bufnr integer
---@param placement ow.Git.StatusView.Placement
local function set_keymaps(bufnr, placement)
    if placement == "sidebar" then
        vim.keymap.set("n", "<Tab>", function()
            preview_or_open(false)
        end, { buffer = bufnr, silent = true, desc = "Preview diff" })
    else
        pcall(vim.keymap.del, "n", "<Tab>", { buffer = bufnr })
    end
end

---@class ow.Git.StatusView.OpenOpts
---@field placement ow.Git.StatusView.Placement?

---@param opts? ow.Git.StatusView.OpenOpts
function M.open(opts)
    opts = opts or {}
    local placement = opts.placement or "sidebar"
    if not vim.tbl_contains(M.PLACEMENTS, placement) then
        util.error(
            "invalid placement: %s (expected one of %s)",
            placement,
            table.concat(M.PLACEMENTS, ", ")
        )
        return
    end
    local r = repo.resolve()
    if not r then
        util.error("not in a git repository")
        return
    end

    local previous_win = vim.api.nvim_get_current_win()
    local buf = vim.fn.bufadd(buf_name_for(r))

    local visible = vim.fn.bufwinid(buf)
    if visible ~= -1 then
        vim.api.nvim_set_current_win(visible)
        r:refresh()
        return
    end

    if not state[buf] then
        vim.fn.bufload(buf)
        repo.bind(buf, r)
        util.setup_scratch(buf, {})
        vim.bo[buf].filetype = "gitstatus"
        setup_buffer(buf, r, placement)
    end
    vim.bo[buf].bufhidden = placement == "sidebar" and "wipe" or "hide"

    local win = place(buf, placement)
    state[buf].win = win
    state[buf].placement = placement
    set_keymaps(buf, placement)

    if placement == "sidebar" then
        vim.api.nvim_set_current_win(previous_win)
    end

    refresh(buf)
    r:refresh()
end

---@param opts? ow.Git.StatusView.OpenOpts
function M.toggle(opts)
    local existing = find_view()
    if existing then
        vim.api.nvim_win_close(existing, false)
        return
    end
    M.open(opts)
end

return M