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package main

import (
	"regexp"
	"strconv"
	"strings"
)

// Parsing of `xrandr`'s human-readable output.
//
// These three patterns are a port of the `xrandr-parse` npm package, which this
// tool used to shell out to node for. The whole package was 49 lines, of which
// these regexes were the interesting part, so it is inlined here rather than
// vendored: it removes a GitHub fetch, a node_modules tree assembled by hand out
// of execline and netstrings, and the node runtime itself.
//
// The output of `xrandr` looks like this:
//
//	Screen 0: minimum 320 x 200, current 4480 x 1440, maximum 16384 x 16384
//	eDP connected 1920x1080+0+360 (normal left inverted ...) 309mm x 173mm
//	   1920x1080     60.03*+
//	   1680x1050     60.03
//	HDMI-A-0 disconnected primary 2560x1440+1920+0 (normal ...) 0mm x 0mm
//
// where `*` marks the currently active mode and `+` the preferred ("native") one.
var (
	reConnected    = regexp.MustCompile(`^(\S+) connected (?:(\d+)x(\d+))?`)
	reDisconnected = regexp.MustCompile(`^(\S+) disconnected`)
	// The height may end in `i` for interlaced modes (e.g. `1920x1080i`), so it
	// is not simply `\d+`.
	reMode = regexp.MustCompile(`^\s+(\d+)x([0-9i]+)\s+((?:\d+\.)?\d+)([* ]?)([+ ]?)`)
)

// Mode is a resolution an output supports.
//
// Width and Height are strings, not numbers, because Height can be something
// like "1080i". Keeping both as they were printed also means the JSON produced
// by `monitor parse` is byte-identical to what the old node parser emitted,
// which is what let the two be diffed against each other during the rewrite.
type Mode struct {
	Width  string  `json:"width"`
	Height string  `json:"height"`
	Rate   float64 `json:"rate"`
}

// Output is a single connector (eDP, HDMI-A-0, ...) as xrandr reports it.
type Output struct {
	Name string `json:"-"`

	Connected bool   `json:"connected"`
	Modes     []Mode `json:"modes"`
	Index     int    `json:"index"`

	// Width and Height are the dimensions from the connector line itself
	// (`1920x1080+0+360`). Only present when xrandr printed them, which is why
	// they are pointers: a disconnected output has none, and emitting `0` would
	// be a lie rather than an absence.
	Width  *int `json:"width,omitempty"`
	Height *int `json:"height,omitempty"`

	// Native is the mode marked `+` (preferred), Current the one marked `*`
	// (active). Either can be absent.
	Native  *Mode `json:"native,omitempty"`
	Current *Mode `json:"current,omitempty"`
}

// Parse turns the output of `xrandr` into a list of outputs, in the order
// xrandr printed them.
//
// Note that `connected` is taken from the literal keyword and nothing else. An
// output can be reported as `disconnected` while still carrying a resolution
// and even `primary` -- this happens on rolery with HDMI-A-0 -- and treating
// "has a resolution" as "is connected" would pick a monitor that is not there.
func Parse(xrandrOutput string) []Output {
	var outputs []Output
	// Index of the output that mode lines currently attach to, or -1 for none.
	last := -1

	for _, line := range strings.Split(xrandrOutput, "\n") {
		if m := reConnected.FindStringSubmatch(line); m != nil {
			out := Output{Name: m[1], Connected: true, Modes: []Mode{}, Index: len(outputs)}
			// Groups 2 and 3 are optional: `<name> connected` with no geometry.
			if m[2] != "" && m[3] != "" {
				w, errW := strconv.Atoi(m[2])
				h, errH := strconv.Atoi(m[3])
				if errW == nil && errH == nil {
					out.Width, out.Height = &w, &h
				}
			}
			outputs = append(outputs, out)
			last = len(outputs) - 1
			continue
		}

		if m := reDisconnected.FindStringSubmatch(line); m != nil {
			outputs = append(outputs, Output{
				Name: m[1], Connected: false, Modes: []Mode{}, Index: len(outputs),
			})
			last = len(outputs) - 1
			continue
		}

		if last >= 0 {
			if m := reMode.FindStringSubmatch(line); m != nil {
				// The rate always parses: the regex only matches digits and at
				// most one dot.
				rate, err := strconv.ParseFloat(m[3], 64)
				if err != nil {
					continue
				}
				mode := Mode{Width: m[1], Height: m[2], Rate: rate}

				o := &outputs[last]
				o.Modes = append(o.Modes, mode)
				// `*` and `+` may appear in either order, hence checking both
				// groups for each marker.
				if m[4] == "+" || m[5] == "+" {
					m := mode
					o.Native = &m
				}
				if m[4] == "*" || m[5] == "*" {
					m := mode
					o.Current = &m
				}
				continue
			}
		}

		// Any line that is neither a connector nor a mode ends the current
		// output. This is load-bearing: it is what stops the indented modeline
		// blocks that `xrandr --verbose` prints
		//
		//	  2560x1440 (0x60) 241.500MHz +HSync -VSync
		//	        h: width  2560 start 2608 end 2640 ...
		//
		// from being attached as modes to whichever output came last.
		last = -1
	}

	return outputs
}

// Connected returns only the outputs xrandr called `connected`.
func Connected(outputs []Output) []Output {
	var connected []Output
	for _, o := range outputs {
		if o.Connected {
			connected = append(connected, o)
		}
	}
	return connected
}

// Find returns the output with the given connector name.
func Find(outputs []Output, name string) (Output, bool) {
	for _, o := range outputs {
		if o.Name == name {
			return o, true
		}
	}
	return Output{}, false
}