// Package readings is the single entry point the CLI and TUI use to resolve a
// day's readings. It computes them offline from the embedded calendar engine
// and lectionary data (Ordinary Form when cfg.Lectionary is "new", the 1962
// Extraordinary Form when "traditional"), then applies part filtering, returning
// source-agnostic liturgy.Section values.
package readings

import (
	"strings"

	"github.com/lukaszkasprzak/lectio/internal/config"
	"github.com/lukaszkasprzak/lectio/internal/liturgy"
)

// Options controls how Load resolves a day's readings.
type Options struct {
	// Date is the day to load, formatted YYYY-MM-DD.
	Date string
	// All, when true, keeps every part the config doesn't explicitly hide;
	// when false, only the gospel is kept.
	All bool
}

// Load computes the day's sections and its DayInfo (celebration name,
// liturgical colour -- see liturgy.DayInfo) for the configured form
// (cfg.Lectionary: "traditional" or "new") and applies part filtering. Every
// reading is resolved offline from the embedded calendar and lectionary data.
//
// Load is LoadWith(Prepare(cfg), cfg, opts) -- a single call's worth of
// convenience. A caller resolving several dates against the same cfg (a
// week/month view) should call Prepare once and use LoadWith directly instead
// of paying Prepare's cost on every date; see Prepared's doc comment
// (internal/readings/offline.go).
func Load(cfg config.Config, opts Options) ([]liturgy.Section, liturgy.DayInfo, error) {
	return LoadWith(Prepare(cfg), cfg, opts)
}

// LoadWith is Load, given an already-built Prepared (see Prepare) instead of
// building its own. Reuse one Prepared across every date resolved against the
// same cfg to skip re-stacking the calendar layers and re-parsing the book
// table per date -- the fast path mobile.Days's multi-day loop uses.
func LoadWith(p Prepared, cfg config.Config, opts Options) ([]liturgy.Section, liturgy.DayInfo, error) {
	secs, info, err := offlineLoadWith(p, cfg, opts.Date)
	if err != nil {
		return nil, liturgy.DayInfo{}, err
	}
	return filterParts(secs, cfg, opts.All), info, nil
}

// GospelCitation returns the gospel's scripture reference from loaded sections:
// the section tagged "ewangelia" (modern) or "evangelium" (traditional), else
// the first section; preferring its Citation, else the reference parsed from its
// heading. Used by the month-calendar export (and mirrors the CLI helper).
func GospelCitation(secs []liturgy.Section) string {
	pick := func(s liturgy.Section) string {
		if s.Citation != "" {
			return s.Citation
		}
		if c, err := liturgy.ExtractCitation(s.Heading); err == nil {
			return c
		}
		return ""
	}
	for _, s := range secs {
		if s.PartID == "ewangelia" || s.PartID == "evangelium" {
			return pick(s)
		}
	}
	if len(secs) > 0 {
		return pick(secs[0])
	}
	return ""
}

// filterParts keeps only the gospel when !all (PartID "ewangelia" modern or
// "evangelium" traditional). When all and the lectionary is traditional, it
// keeps only the scripture readings (isTraditionalReading) -- dropping
// Introit/Kolekta/Graduale/Offertorium/Sekreta/Prefacja/Komunia/Pokomunia
// and any commemoration, none of which are readings; the "new" lectionary
// path is unchanged, keeping sections cfg.PartShown allows (a section with
// an empty PartID is always kept). Pure and network-free.
func filterParts(secs []liturgy.Section, cfg config.Config, all bool) []liturgy.Section {
	var out []liturgy.Section
	for _, s := range secs {
		if !all {
			if s.PartID == "ewangelia" || s.PartID == "evangelium" {
				out = append(out, s)
			}
			continue
		}
		if cfg.Lectionary == "traditional" {
			if isTraditionalReading(s.PartID) {
				out = append(out, s)
			}
			continue
		}
		if s.PartID == "" || cfg.PartShown(cfg.Lectionary, s.PartID) {
			out = append(out, s)
		}
	}
	return out
}

// isTraditionalReading reports whether partID (a lowercased missalemeum
// section id) is a scripture reading -- the gospel, or an epistle/lesson --
// rather than Introit/Kolekta/Graduale/Offertorium/Sekreta/Prefacja/
// Komunia/Pokomunia or a commemoration.
func isTraditionalReading(partID string) bool {
	return partID == "evangelium" ||
		strings.HasPrefix(partID, "lectio") ||
		strings.HasPrefix(partID, "epistola") ||
		strings.HasPrefix(partID, "prophetia")
}