---@param msg string
local notify_warn = function(msg)
    ya.notify { title = "ZFS", content = msg, level = "warn", timeout = 5 }
end

---@param msg string
local notify_error = function(msg)
    ya.notify { title = "ZFS", content = msg, level = "error", timeout = 5 }
end

---@param arr table
---@param predicate fun(value: any): boolean
---@return number|nil # index if found, nil if not found
local find_index = function(arr, predicate)
    for i, value in ipairs(arr) do
        if predicate(value) then
            return i
        end
    end
    return nil
end

--- Verify if `sudo` is already authenticated
--- @return boolean
local function sudo_already()
    local status = Command("sudo"):args({ "--validate", "--non-interactive" }):status()
    assert(status, "Failed to run `sudo --validate --non-interactive`")
    return status.success
end

--- Run a program with `sudo` privilege
--- @param program string
--- @param args table
--- @return Output|nil output
--- @return integer|nil err
---  nil: no error
---  1: sudo failed
local function run_with_sudo(program, args)
    local cmd = Command("sudo"):args({ program, table.unpack(args) }):stdout(Command.PIPED):stderr(Command.PIPED)
    if sudo_already() then
        return cmd:output()
    end

    local permit = ya.hide()
    print(string.format("Sudo password required to run: `%s %s`", program, table.concat(args, " ")))
    local output = cmd:output()
    permit:drop()

    if output.status.success or sudo_already() then
        return output
    end
    return nil, 1
end


---@return string
local get_cwd = ya.sync(function()
    return tostring(cx.active.current.cwd)
end)

---@param s string
---@return string
local trim = function(s)
    return s:match("^%s*(.-)%s*$")
end

---@param cwd string
---@return string|nil
local get_filesystem_type = function(cwd)
    local stat, _ = Command("stat"):args({ "-f", "-c", "%T", cwd }):output()
    if not stat.status.success then
        return nil
    end
    return trim(stat.stdout)
end

---@param cwd string
---@return string|nil
local zfs_dataset = function(cwd)
    local df, _ = Command("df"):args({ "--output=source", cwd }):output()
    local dataset = nil
    for line in df.stdout:gmatch("[^\r\n]+") do
        -- dataset is last line in output
        dataset = line
    end
    return dataset
end

---@param dataset string
---@return string|nil
local zfs_mountpoint = function(dataset)
    local zfs, _ = Command("zfs"):args({ "get", "-H", "-o", "value", "mountpoint", dataset }):output()

    -- not a dataset!
    if not zfs.status.success then
        return nil
    end

    -- legacy mountpoint, search for actual mountpoint using df
    if zfs.stdout == "legacy\n" then
        local df, _ = Command("df"):output()
        if not df.status.success then
            return nil
        end

        for line in df.stdout:gmatch("[^\r\n]+") do
            -- match start of line
            if string.sub(line, 1, #dataset) == dataset then
                local mountpoint = nil
                for field in line:gmatch("%S+") do
                    -- mountpoint is last field in df output
                    mountpoint = field
                end
                return mountpoint
            end
        end
    else
        return zfs.stdout:gsub("\n$", "")
    end

    -- shouldn't be here
    return nil
end

-- returns the path relative to the mountpoint / snapshot
---@param cwd string
---@param mountpoint string
local zfs_relative = function(cwd, mountpoint)
    -- relative path to get mountpoint
    local relative = (cwd:sub(0, #mountpoint) == mountpoint) and cwd:sub(#mountpoint + 1) or cwd

    -- is a snapshot dir, strip everything after "/snapshot"
    if cwd:find(".zfs/snapshot") ~= nil then
        local snapshot_pos = cwd:find("/snapshot")

        -- everything after the "/snapshot/"
        local after = cwd:sub(snapshot_pos + #"/snapshot" + 1)
        local first_slash = after:find("/")
        -- root of snapshot?
        if first_slash == nil then
            return "/"
        else
            return after:sub(first_slash)
        end
    end

    return relative
end

---@class Snapshot
---@field name string
---@field path string

---@param dataset string
---@param mountpoint string
---@param relative string
---@return Snapshot[]
local zfs_snapshots = function(dataset, mountpoint, relative)
    -- -S is for reverse order
    local zfs_snapshots, _ = Command("zfs"):args({ "list", "-H", "-t", "snapshot", "-o", "name", "-S", "creation",
            dataset })
        :output()

    if not zfs_snapshots.status.success then
        return {}
    end

    ---@type Snapshot[]
    local snapshots = {}
    for snapshot in zfs_snapshots.stdout:gmatch("[^\r\n]+") do
        -- in the format dataset@snapshot
        local sep = snapshot:find("@")
        local id = snapshot:sub(sep + 1)

        table.insert(snapshots, {
            id = id,
            path = mountpoint .. "/.zfs/snapshot/" .. id .. relative,
        })
    end
    return snapshots
end

---@param cwd string
---@return string|nil
local function btrfs_mountpoint(cwd)
    local cmd, _ = Command("findmnt"):args({ "-no", "TARGET", "-T", cwd }):output()
    if not cmd.status.success then
        return nil
    end
    return trim(cmd.stdout)
end

---Returns the current uuid and the parent uuid
---@param cwd string
---@return string|nil, string|nil
local function btrfs_uuids(cwd)
    local cmd, _ = run_with_sudo("btrfs", { "subvolume", "show", cwd })
    if not cmd then
        return nil
    end

    local parent_uuid = nil
    local uuid = nil
    for line in cmd.stdout:gmatch("[^\r\n]+") do
        local parent_uuid_re = line:match("^%s*Parent UUID:%s*(%S+)")
        if parent_uuid_re then
            parent_uuid = trim(parent_uuid_re)
        end

        local uuid_re = line:match("^%s*UUID:%s*(%S+)")
        if uuid_re then
            uuid = trim(uuid_re)
        end
    end
    return parent_uuid, uuid
end

---@param mountpoint string
---@param current_uuid string
---@param current_parent_uuid string|nil
---@return { snapshots: Snapshot[], latest_path: string, current_snapshot_id: string }
local function btrfs_snapshots(mountpoint, current_uuid, current_parent_uuid)
    local snapshots_cmd, _ = run_with_sudo("btrfs", { "subvolume", "list", "-q", "-u", mountpoint })
    if not snapshots_cmd then
        return {}
    end

    local snapshots = {}
    local latest_path = ""
    local current_snapshot_id = ""

    for line in snapshots_cmd.stdout:gmatch("[^\r\n]+") do
        local pattern = "ID (%d+) gen %d+ top level %d+ parent_uuid ([%w-]+)%s+uuid ([%w-]+) path (%S+)"
        -- Extract the fields
        local subvol_id, parent_uuid, uuid, name = line:match(pattern)
        parent_uuid = trim(parent_uuid)

        local path = mountpoint .. "/" .. name
        local is_parent = false

        if current_parent_uuid == "-" then
            if parent_uuid == "-" and uuid == current_uuid then
                is_parent = true
            end
        else
            if uuid == current_parent_uuid then
                is_parent = true
            end
        end

        if is_parent then
            latest_path = path
        end

        if uuid == current_uuid and not is_parent then
            current_snapshot_id = name
        end

        if not is_parent then
            table.insert(snapshots, {
                id = name,
                subvol_id = subvol_id, -- used only for sorting
                path = path,
            })
        end
    end

    -- Sort snapshots by time descending
    table.sort(snapshots, function(a, b)
        return a.subvol_id > b.subvol_id
    end)

    return { snapshots = snapshots, latest_path = latest_path, current_snapshot_id = current_snapshot_id }
end

return {
    entry = function(_, job)
        local action = job.args[1]
        local cwd = get_cwd()

        if action ~= "exit" and action ~= "prev" and action ~= "next" then
            return notify_error("Invalid action: " .. action)
        end

        local fs_type = get_filesystem_type(cwd)
        if fs_type ~= "zfs" and fs_type ~= "btrfs" then
            return notify_error("Current directory is not on a BTRFS / ZFS filesystem.")
        end

        local current_snapshot_id = ""
        local latest_path = ""
        local snapshots = {}

        if fs_type == "zfs" then
            local dataset = zfs_dataset(cwd)
            if dataset == nil then
                return notify_error("Current directory is not within a ZFS dataset.")
            end

            if cwd:find(".zfs/snapshot") ~= nil then
                -- in the format dataset@snapshot
                local sep = dataset:find("@")
                current_snapshot_id = dataset:sub(sep + 1)
                dataset = dataset:sub(1, sep - 1)
            end

            local mountpoint = zfs_mountpoint(dataset)
            if mountpoint == nil then
                return notify_error("Current directory is not within a ZFS dataset.")
            end

            -- NOTE: relative already has leading "/"
            local relative = zfs_relative(cwd, mountpoint)

            latest_path = mountpoint .. relative
            snapshots = zfs_snapshots(dataset, mountpoint, relative)
        elseif fs_type == "btrfs" then
            local mountpoint = btrfs_mountpoint(cwd)
            local parent_uuid, uuid = btrfs_uuids(cwd)

            if mountpoint == nil or uuid == nil then
                return notify_error("Current directory is not within a BTRFS subvolume.")
            end

            local ret = btrfs_snapshots(mountpoint, uuid, parent_uuid)
            snapshots = ret.snapshots
            latest_path = ret.latest_path
            current_snapshot_id = ret.current_snapshot_id
        end

        if action == "exit" then
            ya.manager_emit("cd", { latest_path })
            return
        end

        if #snapshots == 0 then
            return notify_warn("No snapshots found.")
        end

        ---@param start_idx integer
        ---@param end_idx integer
        ---@param step integer
        local find_and_goto_snapshot = function(start_idx, end_idx, step)
            if start_idx == 0 then
                -- going from newest snapshot to current state
                return ya.manager_emit("cd", { latest_path })
            elseif start_idx < 0 then
                return notify_warn("No earlier snapshots found.")
            elseif start_idx > #snapshots then
                return notify_warn("No earlier snapshots found.")
            end

            for i = start_idx, end_idx, step do
                local snapshot_dir = snapshots[i].path
                if io.open(snapshot_dir, "r") then
                    return ya.manager_emit("cd", { snapshot_dir })
                end
            end

            local direction = action == "prev" and "earlier" or "later"
            return notify_warn("No " .. direction .. " snapshots found.")
        end

        -- NOTE: latest snapshot is first in list
        if current_snapshot_id == "" then
            if action == "prev" then
                -- go to latest snapshot
                return find_and_goto_snapshot(1, #snapshots, 1)
            elseif action == "next" then
                return notify_warn("No later snapshots found.")
            end
        end

        -- has current snapshot
        local idx = find_index(snapshots, function(snapshot) return snapshot.id == current_snapshot_id end)
        if idx == nil then
            return notify_error("Snapshot not found.")
        end

        if action == "prev" then
            find_and_goto_snapshot(idx + 1, #snapshots, 1)
        elseif action == "next" then
            find_and_goto_snapshot(idx - 1, 1, -1)
        end
    end,
}