From b1c5b729d17905cfaef32b57edaa7b51a35317af Mon Sep 17 00:00:00 2001
From: gutmet <me.git@gutmet.org>
Date: Sun, 14 Jun 2020 11:06:20 +0200
Subject: [PATCH] fix trend calculation if days are missing by linear
 interpolation

---
 hdiet.go | 76 ++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 60 insertions(+), 16 deletions(-)

diff --git a/hdiet.go b/hdiet.go
index d7261aa..7dc3560 100644
--- a/hdiet.go
+++ b/hdiet.go
@@ -102,14 +102,21 @@ type yRange struct {
 	max float64
 }
 
-func process(file string) ([]point, error) {
+func readFile(file string) (map[time.Time]float64, time.Time, time.Time) {
+	optPanic := func(err error) {
+		if err != nil {
+			panic("process:" + err.Error())
+		}
+	}
 	weights, err := goutil.ReadFile(file)
 	if err != nil {
-		return nil, err
+		return nil, time.Time{}, time.Time{}
 	}
 	lines := strings.Split(weights, "\n")
-	trend := 0.0
-	s := []point{}
+	var firstDay time.Time
+	firstDayIsSet := false
+	var lastDay time.Time
+	dateToWeight := make(map[time.Time]float64)
 	for _, line := range lines {
 		line = strings.TrimSpace(line)
 		if len(line) == 0 {
@@ -117,18 +124,58 @@ func process(file string) ([]point, error) {
 		}
 		splitline := strings.Split(line, "\t")
 		if len(splitline) < 2 {
-			return nil, errors.New("process - invalid line in weight file: " + line)
+			optPanic(errors.New("invalid line in weight file " + file + ": " + line))
+		}
+		date, err := time.Parse(dateLayout, splitline[0])
+		optPanic(err)
+		weight, err := strconv.ParseFloat(splitline[1], 64)
+		optPanic(err)
+		if !firstDayIsSet {
+			firstDay = date
+			firstDayIsSet = true
+		}
+		lastDay = date
+		dateToWeight[date] = weight
+	}
+	return dateToWeight, firstDay, lastDay
+}
+
+func process(file string) []point {
+	dateToWeight, firstDay, lastDay := readFile(file)
+	if dateToWeight == nil {
+		return []point{}
+	}
+	trend := 0.0
+	points := []point{}
+	for d := firstDay; d.Before(lastDay) || d == lastDay; d = d.AddDate(0, 0, 1) {
+		var weight float64
+		if w, ok := dateToWeight[d]; ok {
+			weight = w
+		} else {
+			prevPoint := points[len(points)-1]
+			prevDay := prevPoint.date
+			prevWeight := prevPoint.weight
+			var nextWeight float64
+			var nextDay time.Time
+			for nextDay = d.AddDate(0, 0, 1); nextDay.Before(lastDay) || nextDay == lastDay; nextDay = nextDay.AddDate(0, 0, 1) {
+				if w, ok := dateToWeight[nextDay]; ok {
+					nextWeight = w
+					break
+				}
+			}
+			days := nextDay.Sub(prevDay).Hours() / 24
+			changePerDay := (nextWeight - prevWeight) / days
+			weight = prevWeight + changePerDay
 		}
-		date, _ := time.Parse(dateLayout, splitline[0])
-		weight, _ := strconv.ParseFloat(splitline[1], 64)
 		if trend == 0.0 {
 			trend = weight
 		} else {
 			trend = math.Floor((trend+0.1*(weight-trend))*100) / 100
 		}
-		s = append(s, point{date, weight, trend})
+		points = append(points, point{d, weight, trend})
+
 	}
-	return s, nil
+	return points
 }
 
 type showFlags struct {
@@ -138,11 +185,8 @@ type showFlags struct {
 }
 
 func show(args showFlags) error {
-	points, err := process(logfile)
-	if err != nil {
-		return err
-	}
-	dietpoints, _ := process(dietfile)
+	points := process(logfile)
+	dietpoints := process(dietfile)
 	var to time.Time
 	var from time.Time
 	if args.to.date != nil {
@@ -170,7 +214,7 @@ func show(args showFlags) error {
 	YRange.min = math.Floor(YRange.min) - 1.0
 	YRange.max = math.Ceil(YRange.max) + 1.0
 	graph := graph(xticks(xRange), s1, s2, s3, YRange)
-	err = writeGraphToFile(graph)
+	err := writeGraphToFile(graph)
 	if err != nil {
 		return err
 	}
@@ -194,7 +238,7 @@ func showCommand() (goutil.CommandFlagsInit, goutil.CommandFunc) {
 func writeDietFile(from time.Time, initial float64, goal float64, change float64) error {
 	date := from
 	weight := initial
-	s := "#Date\tTarget\n"
+	s := ""
 	s += fmt.Sprintf("%s\t%.1f\n", date.Format(dateLayout), weight)
 	for weight > goal {
 		date = date.AddDate(0, 0, 1)