local commit = require("git.commit")
local object = require("git.object")
local repo = require("git.repo")
local util = require("git.util")

local M = {}

---@class ow.Git.Cmd.SplitHandler
---@field ft string
---@field needs_rev boolean?

---@type table<string, ow.Git.Cmd.SplitHandler>
local SPLIT_HANDLERS = {
    log = { ft = "git" },
    diff = { ft = "diff" },
}

---@type string[]?
local cached_cmds

---@return string[]
local function git_cmds()
    if cached_cmds then
        return cached_cmds
    end
    local result = vim.system(
        { "git", "--list-cmds=main,others,alias" },
        { text = true }
    )
        :wait()
    if result.code ~= 0 then
        util.error("git --list-cmds failed: %s", vim.trim(result.stderr or ""))
        return {}
    end
    cached_cmds = {}
    for line in (result.stdout or ""):gmatch("[^\r\n]+") do
        if line ~= "" then
            table.insert(cached_cmds, line)
        end
    end
    table.sort(cached_cmds)
    return cached_cmds
end

---@param tok string
---@return boolean
local function is_expansion_target(tok)
    local first = tok:sub(1, 1)
    if first == "%" or first == "#" then
        return true
    end
    if tok:match("^<%w+>") then
        return true
    end
    if tok == "~" or tok:sub(1, 2) == "~/" then
        return true
    end
    return false
end

---@param line string
---@param i integer
---@param buf string[]
---@param escapes string?
---@return integer
local function parse_quoted(line, i, buf, escapes)
    local quote = line:sub(i, i)
    local n = #line
    i = i + 1
    while i <= n do
        local c = line:sub(i, i)
        if c == quote then
            return i + 1
        elseif escapes and c == "\\" and i < n then
            local nxt = line:sub(i + 1, i + 1)
            if escapes:find(nxt, 1, true) then
                table.insert(buf, nxt)
                i = i + 2
            else
                table.insert(buf, c)
                i = i + 1
            end
        else
            table.insert(buf, c)
            i = i + 1
        end
    end
    return i
end

---@param line string
---@return string[]
function M.parse_args(line)
    local args = {}
    local i, n = 1, #line
    while i <= n do
        local c = line:sub(i, i)
        if c == " " or c == "\t" then
            i = i + 1
        else
            local buf = {}
            local quoted = false
            while i <= n do
                c = line:sub(i, i)
                if c == " " or c == "\t" then
                    break
                elseif c == "\\" and i < n then
                    table.insert(buf, line:sub(i + 1, i + 1))
                    i = i + 2
                elseif c == '"' then
                    quoted = true
                    i = parse_quoted(line, i, buf, '"\\$`')
                elseif c == "'" then
                    quoted = true
                    i = parse_quoted(line, i, buf, nil)
                else
                    table.insert(buf, c)
                    i = i + 1
                end
            end
            local tok = table.concat(buf)
            if not quoted and is_expansion_target(tok) then
                local expanded = vim.fn.expand(tok) --[[@as string]]
                if expanded ~= "" then
                    tok = expanded
                end
            end
            table.insert(args, tok)
        end
    end
    return args
end

---@param args string[]
---@param start integer
---@return string?
local function first_positional(args, start)
    for i = start, #args do
        local a = args[i]
        if a:sub(1, 1) ~= "-" then
            return a
        end
    end
end

---@param name string
---@return integer buf
local function place_split(name)
    local buf = vim.fn.bufnr("\\V" .. name)
    if buf == -1 or not vim.api.nvim_buf_is_loaded(buf) then
        buf = util.new_scratch()
        pcall(vim.api.nvim_buf_set_name, buf, name)
        return buf
    end
    local win_id = vim.fn.bufwinid(buf)
    if win_id ~= -1 then
        vim.api.nvim_set_current_win(win_id)
    else
        util.place_buf(buf, nil)
    end
    return buf
end

---@param r ow.Git.Repo
---@param args string[]
---@param conf ow.Git.Cmd.SplitHandler
local function run_in_split(r, args, conf)
    local cmd = { "git" }
    vim.list_extend(cmd, args)
    util.exec(cmd, {
        cwd = r.worktree,
        on_done = function(stdout)
            if not stdout then
                return
            end
            local name = "[git " .. table.concat(args, " ") .. "]"
            local buf = place_split(name)
            repo.bind(buf, r)
            object.attach_dispatch(buf)
            local state = r:state(buf) --[[@as -nil]]
            state.sha = nil
            state.parent_sha = nil
            if conf.needs_rev then
                local user_rev = first_positional(args, 2) or "HEAD"
                local sha = r:rev_parse(user_rev, true)
                if sha then
                    state.sha = sha
                    state.parent_sha = r:rev_parse(user_rev .. "^", true)
                end
            end
            vim.bo[buf].filetype = conf.ft
            util.set_buf_lines(buf, 0, -1, util.split_lines(stdout))
        end,
    })
end

---@param r ow.Git.Repo
---@param args string[]
local function run_to_messages(r, args)
    local cmd = { "git" }
    vim.list_extend(cmd, args)
    vim.system(
        cmd,
        { cwd = r.worktree, text = true },
        vim.schedule_wrap(function(obj)
            local out = vim.trim(obj.stdout or "")
            local err = vim.trim(obj.stderr or "")
            local chunks = {}
            if out ~= "" then
                table.insert(chunks, { out })
            end
            if err ~= "" then
                if #chunks > 0 then
                    table.insert(chunks, { "\n" })
                end
                table.insert(chunks, { err, "ErrorMsg" })
            end
            if #chunks == 0 and obj.code ~= 0 then
                table.insert(
                    chunks,
                    { "git exited " .. tostring(obj.code), "ErrorMsg" }
                )
            end
            if #chunks > 0 then
                vim.api.nvim_echo(chunks, true, {})
            end
        end)
    )
end

---@param args string[]
---@return boolean
local function has_message(args)
    for _, a in ipairs(args) do
        if
            a == "-m"
            or a == "--message"
            or a:match("^%-%-message=")
            or a:match("^%-m")
        then
            return true
        end
    end
    return false
end

---@param args string[]
function M.run(args)
    local r = repo.resolve()
    if not r then
        util.error("not in a git repository")
        return
    end

    local sub = args[1]
    if sub == "commit" and not has_message(args) then
        commit.commit({ args = vim.list_slice(args, 2) })
        return
    end

    if sub == "show" then
        if #args == 2 and args[2]:find(":", 1, true) then
            object.open(r, args[2])
            return
        end
        run_in_split(r, args, { ft = "git", needs_rev = true })
        return
    end

    if sub == "cat-file" then
        if #args == 3 and args[2] == "-p" then
            object.open(r, args[3])
            return
        end
        run_in_split(r, args, { ft = "git", needs_rev = true })
        return
    end

    local conf = sub and SPLIT_HANDLERS[sub]
    if conf then
        run_in_split(r, args, conf)
    else
        run_to_messages(r, args)
    end
end

---@param items string[]
---@param lead string
---@return string[]
local function prefix_filter(items, lead)
    return vim.tbl_filter(function(it)
        return vim.startswith(it, lead)
    end, items)
end

---@param prefix string
---@param dir string
---@param name_lead string
---@param entries string[]
---@return string[]
local function path_segments(prefix, dir, name_lead, entries)
    local matches = {}
    local seen = {}
    for _, full_path in ipairs(entries) do
        local rel = dir == "" and full_path or full_path:sub(#dir + 1)
        local slash = rel:find("/", 1, true)
        local segment = slash and rel:sub(1, slash) or rel
        if not seen[segment] and segment:sub(1, #name_lead) == name_lead then
            seen[segment] = true
            table.insert(matches, prefix .. dir .. segment)
        end
    end
    return matches
end

---@param r ow.Git.Repo
---@param dir string
---@return string[]
local function list_files(r, dir)
    local cmd = { "git", "ls-files" }
    if dir ~= "" then
        table.insert(cmd, dir)
    end
    local out = util.exec(cmd, { cwd = r.worktree, silent = true })
    return out and util.split_lines(out) or {}
end

---@param r ow.Git.Repo
---@return string[]
local function list_remotes(r)
    local out = util.exec(
        { "git", "remote" },
        { cwd = r.worktree, silent = true }
    )
    return out and util.split_lines(out) or {}
end

---@type table<string, string[]>
local SUBSUB_FALLBACK = {
    submodule = {
        "add",
        "status",
        "init",
        "deinit",
        "update",
        "summary",
        "foreach",
        "sync",
        "absorbgitdirs",
    },
}

---@type table<string, string[]>
local cached_completions = {}

---@param sub string
---@return string[]
local function fetch_completions(sub)
    if cached_completions[sub] then
        return cached_completions[sub]
    end
    local out = util.exec(
        { "git", sub, "--git-completion-helper-all" },
        { silent = true }
    ) or util.exec(
        { "git", sub, "--git-completion-helper" },
        { silent = true }
    )
    local items = {}
    if out then
        for tok in out:gmatch("%S+") do
            table.insert(items, tok)
        end
    end
    cached_completions[sub] = items
    return items
end

---@param sub string
---@return string[]
local function fetch_subsubcommands(sub)
    local subs = {}
    for _, it in ipairs(fetch_completions(sub)) do
        if it:sub(1, 1) ~= "-" and it ~= "--" then
            table.insert(subs, it)
        end
    end
    if #subs == 0 and SUBSUB_FALLBACK[sub] then
        return SUBSUB_FALLBACK[sub]
    end
    return subs
end

---@param sub string
---@return string[]
local function fetch_flags(sub)
    local flags = {}
    for _, it in ipairs(fetch_completions(sub)) do
        if it:sub(1, 1) == "-" and it ~= "--" then
            table.insert(flags, it)
        end
    end
    return flags
end

---@param r ow.Git.Repo
---@param lead string
---@return string[]
local function complete_tracked_paths(r, lead)
    local dir, name_lead = lead:match("^(.*/)([^/]*)$")
    dir = dir or ""
    name_lead = name_lead or lead
    return path_segments("", dir, name_lead, list_files(r, dir))
end

---@param r ow.Git.Repo
---@param lead string
---@return string[]
local function complete_unstaged_paths(r, lead)
    local matches = {}
    for path, entry_list in pairs(r.status.entries) do
        if path:sub(1, #lead) == lead then
            for _, e in ipairs(entry_list) do
                if
                    e.kind == "unstaged"
                    or e.kind == "untracked"
                    or e.kind == "unmerged"
                then
                    table.insert(matches, path)
                    break
                end
            end
        end
    end
    table.sort(matches)
    return matches
end

---@param arg_lead string
---@return string[]
function M.complete_rev(arg_lead)
    local r = repo.resolve()
    if not r then
        return {}
    end

    local stage, stage_path_lead = arg_lead:match("^:([0-3]):(.*)$")
    if stage then
        local out = util.exec(
            { "git", "ls-files", "--stage" },
            { cwd = r.worktree, silent = true }
        )
        if not out then
            return {}
        end
        local matches = {}
        for _, line in ipairs(util.split_lines(out)) do
            local row_stage, row_path = line:match("^%S+ %S+ (%d)\t(.*)$")
            if
                row_stage == stage
                and row_path
                and row_path:sub(1, #stage_path_lead) == stage_path_lead
            then
                table.insert(matches, ":" .. stage .. ":" .. row_path)
            end
        end
        return matches
    end

    local colon = arg_lead:find(":", 1, true)
    if not colon then
        local refs = r:list_refs()
        vim.list_extend(refs, r:list_pseudo_refs())
        vim.list_extend(refs, r:list_stash_refs())
        return prefix_filter(refs, arg_lead)
    end

    local rev = arg_lead:sub(1, colon - 1)
    local path_lead = arg_lead:sub(colon + 1)
    local dir, name_lead = path_lead:match("^(.*/)([^/]*)$")
    dir = dir or ""
    name_lead = name_lead or path_lead

    if rev ~= "" then
        local cmd = { "git", "ls-tree", rev }
        if dir ~= "" then
            table.insert(cmd, dir)
        end
        local out = util.exec(cmd, { cwd = r.worktree, silent = true })
        if not out then
            return {}
        end
        local matches = {}
        for _, line in ipairs(util.split_lines(out)) do
            local typ, full_path = line:match("^%S+ (%S+) %S+\t(.*)$")
            if typ and full_path then
                local basename = dir == "" and full_path
                    or full_path:sub(#dir + 1)
                if typ == "tree" then
                    basename = basename .. "/"
                end
                if basename:sub(1, #name_lead) == name_lead then
                    table.insert(matches, rev .. ":" .. dir .. basename)
                end
            end
        end
        return matches
    end

    return path_segments(":", dir, name_lead, list_files(r, dir))
end

---@alias ow.Git.Cmd.Handler fun(r: ow.Git.Repo, lead: string, sub: string, idx: integer): string[]
---@alias ow.Git.Cmd.Slot ow.Git.Cmd.Handler | ow.Git.Cmd.Handler[]

---@param r ow.Git.Repo
---@param lead string
---@return string[]
local function complete_remote(r, lead)
    return prefix_filter(list_remotes(r), lead)
end

---@param r ow.Git.Repo
---@param lead string
---@return string[]
local function complete_ref(r, lead)
    return prefix_filter(r:list_refs(), lead)
end

---@param r ow.Git.Repo
---@param lead string
---@return string[]
local function complete_pseudo_ref(r, lead)
    return prefix_filter(r:list_pseudo_refs(), lead)
end

---@param r ow.Git.Repo
---@param lead string
---@return string[]
local function complete_stash_ref(r, lead)
    return prefix_filter(r:list_stash_refs(), lead)
end

---@param _ ow.Git.Repo
---@param lead string
---@return string[]
local function complete_rev(_, lead)
    return M.complete_rev(lead)
end

---@param _ ow.Git.Repo
---@param lead string
---@param sub string
---@param idx integer
---@return string[]
local function complete_subsubcmd(_, lead, sub, idx)
    if idx ~= 1 then
        return {}
    end
    return prefix_filter(fetch_subsubcommands(sub), lead)
end

local ALL_REFS = { complete_ref, complete_pseudo_ref, complete_stash_ref }
local REV_OR_PATH = { complete_rev, complete_tracked_paths }

---@type table<string, ow.Git.Cmd.Slot[]>
local POSITIONAL_HANDLER = {
    push = { complete_remote, ALL_REFS },
    pull = { complete_remote, ALL_REFS },
    fetch = { complete_remote, ALL_REFS },
    checkout = { REV_OR_PATH },
    reset = { REV_OR_PATH },
    restore = { complete_tracked_paths },
    add = { complete_unstaged_paths },
    rm = { complete_tracked_paths },
    mv = { complete_tracked_paths },
    blame = { complete_tracked_paths },
    branch = { complete_ref },
    switch = { complete_ref },
    merge = { ALL_REFS },
    rebase = { ALL_REFS },
    ["cherry-pick"] = { ALL_REFS },
    revert = { ALL_REFS },
    tag = { ALL_REFS },
    log = { REV_OR_PATH },
    diff = { REV_OR_PATH },
    show = { complete_rev },
    ["cat-file"] = { complete_rev },
    stash = { complete_subsubcmd },
    remote = { complete_subsubcmd },
    worktree = { complete_subsubcmd },
    bisect = { complete_subsubcmd },
    submodule = { complete_subsubcmd },
}

---@class ow.Git.Cmd.CompleteState
---@field prior string[]  -- positional and flag tokens before the current arg_lead
---@field after_separator boolean  -- whether `--` appeared in prior

---@param cmd_line string
---@return ow.Git.Cmd.CompleteState
local function parse_complete_state(cmd_line)
    local rest = cmd_line:gsub("^%s*%S+%s*", "", 1)
    local trailing_space = rest == "" or rest:sub(-1):match("%s") ~= nil
    local tokens = vim.split(vim.trim(rest), "%s+", { trimempty = true })
    local prior = trailing_space and tokens
        or vim.list_slice(tokens, 1, #tokens - 1)
    local after_separator = false
    for _, t in ipairs(prior) do
        if t == "--" then
            after_separator = true
            break
        end
    end
    return { prior = prior, after_separator = after_separator }
end

---@param prior string[]  -- includes the subcommand at index 1
---@return integer
local function positional_index(prior)
    local pos = 0
    for i = 2, #prior do
        if prior[i]:sub(1, 1) ~= "-" then
            pos = pos + 1
        end
    end
    return pos + 1
end

---@param arg_lead string
---@param cmd_line string
---@return string[]
function M.complete(arg_lead, cmd_line, _)
    local state = parse_complete_state(cmd_line)
    local prior = state.prior

    if #prior == 0 then
        return prefix_filter(git_cmds(), arg_lead)
    end

    local sub = prior[1] --[[@as string]]

    if arg_lead:sub(1, 1) == "-" then
        return prefix_filter(fetch_flags(sub), arg_lead)
    end

    local r = repo.resolve()
    if not r then
        return {}
    end

    if state.after_separator then
        return complete_tracked_paths(r, arg_lead)
    end

    local handlers = POSITIONAL_HANDLER[sub]
    if not handlers then
        return complete_tracked_paths(r, arg_lead)
    end

    local idx = positional_index(prior)
    local slot = handlers[idx] or handlers[#handlers]
    if not slot then
        return {}
    end
    if type(slot) == "function" then
        return slot(r, arg_lead, sub, idx)
    end
    local result = {}
    for _, fn in ipairs(slot) do
        vim.list_extend(result, fn(r, arg_lead, sub, idx))
    end
    return result
end

M._parse_complete_state = parse_complete_state
M._positional_index = positional_index

return M